Oscillating crystal



y 9; 1933- E. D. TILLYER 1,907,613

OSCILLATING CRYSTAL Filed Jan. 12, 1927 Jwuentoc dgarn Iill ez i gfy'wPatented May 9, 1933 UNITED STATES PATENT OFFICE EDGAR I). TILLYER, 0FSOUTHBRIDGE, MASSACHUSETTS, ASSIGNOR TO AMERICAN OPTICAL COMPANY, OFSOUTHBRIDGE, MASSACHUSETTS, A VOLUNTARY ASSOCIA- TION OF MASSACHUSETTSOSCILLATING CRYSTAL Application filed January 12, 1927. Serial No.160,621.

This invention relates to oscillating crystals and more particularly toa crystal to be used in an oscillating circuit or a resonator circuitand to improved means for producing the same.

The principal object of this lnvention 1s to provide a crystal of thisnature that will oscillate efliciently for short waves.

Another object of the invention is to provide a process for cutting sucha crystal so that it will have high efiiciency in oscillation,particularly on short wave lengths,

Another object of the invention is to provide simple, inexpensive andeffic ent means for producing such crystals, reducmgthe cost ofmanufacture of the same, assurlng efliciency and particularly reducingwastage by eliminating the production of non-usuable crystals, as hasoccurred hitherto.

Other objects and advantages of the mvention will become apparent fromthe following description taken in connection with the accompanyingdrawing and it will be understood that many changes may be made in theexact details of construction and the steps of cutting the crystalswithout departing from the spirit of the invention as expressed in theaccompanying claims. I, therefore, do not wish to be limited to theexact details and arrangements of parts and steps of the process shown,the preferred forms only havin been shown by way of illustration.

Iteferring to the drawing,

Figure 1 indicates av portion of a quartz crystal from which Ipreferably manufacture my oscillating crystals;

Figure 2 shows a cross section on line 22 of Figure 1 showing how theprior art crystals were cut and indicating the direction in which theoscillating crystals are cut from the main crystal;

Figure 3 indicates a cross section on line 22 of Figure 1 wherein thedirection in which I cut my oscillating crystals is indicated in dottedlines;

Figure 4 indicates the completed oscillating crystal as cut from thewhole crystal as indicated in Figure 3.

Prior to my invention it has been usual to cut oscillating crystals asindicated in dotted lines in Fig. 2, that is, the sides of theoscillating crystals as out are not parallel with any of the faces ofthe original crystal. It has been found that in crystals cut in this waya large percentage of them, say from seventy to eighty per cent. willnot oscillate on the short Wave lengths and have to be discarded. I havefound, however, that if I cut my oscillating crystals with one faceparallel to a face of the mother crystal, as indicated in dotted linesin Fig. 2, about ninety per cent. of these crystals will give goodresults in those cases where the prior art crystals failed, and that thecrystals so cut are particularly eflicient on the short wave lengths.

Referring to the drawing in which similar reference characters indicatecorresponding parts throughout, I cut my oscillating crystals 1preferably from a quartz crystal 2 with the face of the oscillatingcrystal 1 parallel with a face 3 of the mother crystal. In the quartzmother crystal the broad or longitudinal faces of the crystal areparallel to the optic axis of the crystal. This condi% tion probablyexists in the case of all piezo electric crystals, but the effect of therelationship of the longitudinal face of the crystal to the optic axisis not clearly known and understood. I have, however, found fromexperience with a thousand or more of these oscillating crystals that ifthe longitudinal faces of the oscillating crystal are parallel to thelongitudinal faces of the mother crystal, improved results are obtained.These crystals are cut and finished in the same way as are the prior artcrystals, the difference being that they are cut in a differentdirection and consequently their faces which are placed between theelectrodes of the circuit have a different relation to the faces andoptical axis of the mother crystal than those of the prior art. I havefound from experience that in crystals cut as in the prior art theirgreatest vibration appears to be in their length, width or thickness,but that when out with one side parallel to a face 3 such as I have cutthem their greatest vibration appears to be sidewise or nearly so, thatis, nearly in the direction of their thickness which is the direction inwhich they are used and inserted in the circuit. The wave length inmeters per millimeter of thickness of my crystal is roughly 150, whileout in the method of the prior art it is about 110, indicating thatthere is a difference in the 'mode of vibration between the oscillatingcrystals cut in the two ways, but what this difference is is not knownor understood. This figure of 150 depends somewhat on other dimensionsthan thickness. I have found from experimentation with many of thecrystals cut in my way that the range of this constant is lowest 145 andthe highest 158, although these limits may possibly be exceeded, so thatif it is desired 'to make a crystal which will oscillate at 400 metersthere is a probability that the thickness of the oscillating crystalwill be three millimeters or slightly more, possibly atrifle less,depending on the above value of the constant. The other dimensions ofthis crystal are more or less immaterial, making a slight effect on thewave length. There are indications that the vibration of my crystal isnot in the direction of the length, width or thickness but has an eskeweffect, that is to say, somewhat similar to the movement of the frontand back covers of a book if pushed in a direction parallel to thecovers of the book, that is, one surface would tend to move in onedirection and the opposite surface in the opposite direction, but thisis not definitely known and makes no difference in the operation of thecrystal except that experience has shown that crystals cut in thismanner vibrate differently from those out in the prior art manner andwith much greater freedom and produce much better practical results.With crystals cut as in the prior art vibrations are found in threedimensions, length, width and thickness, whereas in my crystals itappears to be only in one direction, as explained above. There areoccasional nondescript modes of vibration in these crystals as well asin other crystals. These crystals are to provide a constant radiofrequency or to act as a standard of radio frequency in eitheroscillating or in resonator circuits. I have found from experience (agreat number of these crystals having gone into use) that they givedecidedly good results for the short wave lengths and that by cuttingthe crystals in this way I eliminate a great wastage as crystals cut inthe prior art way, as above stated, have failed in from seventy toeighty per cent., wheras in my crystals I get an efliciency of over 90per cent.

The oscillating crystals 1 may be cut from the mother crystal with adiamond saw. with a revolving piece of sheet metal the edge of which ischarged with carborundum, or other abrasive, and in other similar ways.It is not necessary that the direction of out be determined with anygreat precision, simple methods for approximating the same beingsuflicient since small deviations from parallelism with a face of thecrystal, optical axes, etc., do not materially affect the usefulqualities and cgaracteristics of the crystals thereby obtaine The facesof the oscillating crystal cut from and have perfected a method ofproducing this crystal oscillator that eliminates a great" percentage ofthe wastage hitherto found in the production of such crystals, it beingpomted out that crystals of this kind are very expensive. It is adiflicult artirle to produce so that any savings in the production ofthis artlcle 1s of great advantage and a step forward in the art.

Statements herein regarding the direction or plane of cut of crystalsmade in accordance with the invention with reference to the faces of themother crystal, are to be understood as applylng to crystals of typicalshape; and where the optical or Z axes, or the crystallographic or Yaxes, are referred to herein,

these terms are to be lmderstood as used in their ordinary scientificmeanings. The electrlcal or X axes as referred to herein, are to beunderstood as defined by lines extending respectively between theopposite apices of the angles formed by the sides of a typical prismaticmother crystal of approximately regular hexagonal cross section.

Having described my invention, I claim:

1. A piezo-electric element having its electrode faces substantiallyparallel to the optic axls and substantially parallel to one of thelateral faces of the mother crystal.

2. A quartz piezo-electric element ha its electrode faces substantiallyparallel to the optic axis and substantially parallel to one'of thelateral faces of the mother crystal.

3. A piezo electric device comiprising a crystal plate having electrodefaces thereof cut parallel to one of the electrical axes of the; naturalcrystal from which the plate is cu 4. A piezo electric plate cut from aquartz crystal having two substantially parallel electrode faces, theplanes of said electrode faces being substantially arallel to the Z axisand to an X axis thereof.

5. In combination, a piezo-electric crystal section so cut from amother-crystal that the largest surfaces of said section aresubstantially parallel to the optic axis thereof and are approximatelyperpendicular to an ax s which, in the mother crystal, was approximatelyparallel to one of the principal crys- 5 tallographic axes thereof, anda plurality of electrodes associated therewith to constitute anoscillation-controlling device having an oscillation constant of theorder of 130 to 160 meters per millimeter of thickness along the axis towhich said surfaces are perpendicular.

6. A piezo electric element out from a mother crystal of the classdescribed and having its thickness dimension substantially along an axisof crystallization of such mother crystal.

7. A piezo electric element cut from a mother crystal of the classdescribed and having its electrode faces substantially parallel with anelectrical axis of such mother crystal.

EDGAR D. TILLYER.

